But the challenge here is to keep having the American president remain simply the President of the United States of America but have each President aknowledged by the Canadians as their king.
American President is still voted in and he doesn't really have any powers in Canada. He has power in the States and not Canada.
The challenge here is for the Canucks to crown each President King once they get elected.
Alright, I'll bite. Say, the Queen of England pre-arranges a marriage to the president's daughter. The lucky prince escorts her around, and even if most Americans don't really know why the marriage happened, the conspiracy is kinda obvious to the French, who scream bloody murder at the marrying of a royal into a 'common whore', which kinda estranges the Quebec population, who are busy inventing poutine and they do not care so much for the land of snooty people in Louisiana parts of the states.
So, during the wedding, many people are cheering. The Prince and his beautiful wife are used a political marriage, but they do have children, whom they love.
When the QM dies, the Prince moves up, and one of their children is running for New York Congressman. People remember growing up along this boy, seeing his family in the News often, and he's so in because of the media's influence.
After a bit, the King and Queen are replaced by their brood, the King of England marrying a different princess, one from India (all planned to keep the English Empire and the United States in an alliance), and our beloved NY Congressman runs for the Oval Office.
With the new nationalist scene in Canada coming into fashion, the British/American Crown decides to prepare an ambush. They proclaim that the American President will be crowned over Canada, which will have independant status from GB but strong ties.
Any good? I have no real begining date, but it's probably before WW1.